1. Field of the Invention
The present invention relates to image recording apparatus and method of recording an image on a heat-sensitive or thermosensible recording material which has on both sides of a transparent support member a plurality of transparent heat-sensitive color developing layers that develop respective colors in different hues from each other.
2. Description of Prior Art
A heat-sensitive recording method is now known as one of recording an image on recording paper by means of a heating element. Such a heat-sensitive recording method employs a heat-sensitive recording material having a coupler or color former and developer coated on a support member such as paper or synthetic paper, and records an image through the process of heat-processing the heat-sensitive recording material by a thermal head. This type heat-sensitive recording method has recently become more relevant acceleratingly in the fields of monochromatic facsimile devices and printers because of advantages of; (1) no need of development, (2) allowing use of paper that has nature close to normal paper in case of using paper as a support member, (3) easy handling, (4) high color-development density, (5) simple and inexpensive recording apparatus, and (6) less noise than dot printers or so during recording, etc.
In those recording fields, with rapid development of the information industry there has been increased a demand to readily obtain a color hard copy from terminal units of information equipments including computers and facsimile devices. However, multi-coloration of a heat-sensitive recording material requires to incorporate a plurality of color development mechanisms, corresponding to the number of colors to be developed, on the same support member, and control the respective color development mechanisms for separate reactions. In spite of a great deal of efforts devoted in the past, there have not yet been achieved the satisfactory results in hues and separation of the developed colors.
Meanwhile, an opaque support member such as paper or synthetic paper has usually been employed as a support member for the heat-sensitive recording material. This is intended to simply read the color-developed image, as a reflected image, from one side of the support member.
Examples of using a transparent support member for the heat-sensitive recording material are disclosed in Japanese Patent Publication No. 40-20151, and Japanese Patent Application No. 60-68875 and No. 60-184483. These are aimed to obtain a high-contrast image or high-grade quality with an excellent gloss by looking at the heat-recorded image from the side of the transparent support side. There is also proposed such an invention that heat-sensitive recording layers developing different hues from each other are applied on both side of a transparent support member to obtain the color-developed image of two-or multi-colors (see Japanese Patent Application Laid-Open No. 49-114431, No. 50-3640 and No. 60-4092).
However, the heat-sensitive color developing layer of the proposed invention contains a coupling or color forming component and a developing component which are dispersed therein simply in the solid form. In practice, therefor, light scattering makes the color developing layer itself opaque, and the intended multicolor image with sharp color separation cannot be obtained. The invention disclosed in the above Japanese Patent Laid-Open Application No. 60-4092 states the technique of solving the respective components and then coating the resultant solution into the same layer for the purpose of improving transparency of the heat-sensitive color developing layer. But, in this case, the respective components tend to easily develop colors even before printing, thereby resulting in the so-called fogging. Accordingly, the number of separatable colors are small and hence the disclosed heat-sensitive layer is unsatisfactory as a munticolor recording material in its specific nature.
In view of the above, the applicant has previously proposed a multicolor heat-sensitive recording material which includes on both sides of a transparent support plate a plurality of color developing layers that are substantially transparent and develop different hues from each other, and hence which can provide a remarkably excellent image through heat-sensitive color development.
Thus, that heat-sensitive recording material makes it possible to obtain a multicolor image of excellent hue, good color separation and improved image retainment, that could not be obtainable with any prior heat-sensitive recording systems. Also, the image can optionally be provided as either a transmitted image or a reflected image.
This type heat-sensitive recording paper has the color developing layers on both sides thereof, so these both sides have to be heated by thermal heads. Where the color developing multilayers are coated on either side, it is required to first heat the uppermost layer (the layer closest to the surface) for color development with such amount of heat that will not heat-affect the underlying layer(s), and then carry out heating process of the remaining layer(s) after fixing the uppermost colordeveloped layer.
The basic sequence of such image recording will be described below with reference to FIG. 13.
As shown in FIG. 13(A), a heat-sensitive recording material 10 comprises a polyester film 102 (hereafter referred to as PET), as a support member, which has on either side thereof a magenta dye layer 104 (hereinafter referred to as M-dye layer) and a yellow dye layer 106 hereinafter referred to as Y-dye layer formed on the M-dye layer 104. The support member also has, on the other side thereof, a cyan dye layer 108 hereinafter referred to as C-dye layer. All of these dye layers are transparent. The Y-dye layer 106 is of the photo-fixing type. Thus, the Y-dye layer 106 has such nature that it is fixed upon irradiation of light with wavelength of 400 nm from a light source 109, and remains unchanged in color since then even under subsequent heating. A recording head 110 is disposed above the heat-sensitive material 10.
Initially, in FIG. 13(A), the Y-dye layer 106 is heat-processed by the thermal head 110. At this time, the applied amount of heat is selected to the extent that the M-dye layer 104 below the Y-dye layer 106 will not make color development under such heating. Only the Y-dye layer 106 is thereby color-developed.
Then, in FIG. 13(B), light with a wavelength of about 400 nm is irradiated to the support member from the Y-dye layer 106 side, as illustrated. The Y-dye layer 106 is thereby fixed and remain unchanged in color even under subsequent heating.
In FIG. 13(C) the M-dye layer 104 is heat-processed with the larger amount of heat than that applied for heating Y-dye layer 106. This causes the M-dye layer 104 to develop the color.
In FIG. 13(D), the heat-sensitive recording paper 10 is turned upside down, and in FIG. 13(E), the C-dye layer 108 is heat-processed. Where another recording head 112 (see imaginary lines in FIG. 13(A)) is provided below the heat-sensitive recording material 10, the C-dye layer 108 can be heat-processed without reversing the recording paper 10. In either case, the C-dye layer 108 develops the color by applying thereon such amount of heat that will not affect the M-dye layer 104 disposed on the opposite side with the PET 102 therebetween.
As present, however, there has not yet been developed an image recording system which can automatically process the above image recording sequence. As a requirement to implement an image recording system for recording an image on a multicolor heat-sensitive recording material, the heat-sensitive recording material must be positioned accurately to record the same single image in three separate stages for reproducing the color without any shifts or fogging. So long as that requirement cannot be processed automatically, there remains difficulty in achieving the high-speed processing. If the recording heads 110, 112 are disposed one on either side of the heat-sensitive recording material 10 as shown in FIG. 13(A), the operation to reverse the heat-sensitive recording material as shown in FIG. 13(D) can be dispensed with. But such arrangement is not preferable in a practical sense because of an increase in both the number of parts and the size of the apparatus,
Where the heat-sensitive recording material includes a white base coated on the Y-dye layer, a longer interval has to be taken before heat-processing the M-dye layer, resulting in poor operability. The reason of applying the white base is to prevent see-through view of the texture of the heat-sensitive recording material on its rear side and keep the image from losing its clearness. Incidentally, any white pigment may be mixed into the heat-sensitive layer in place of applying the white base separately from the heat-sensitive layer.